The present invention relates to a pneumatic tire for multiple-track vehicles.
Pneumatic tires having an asymmetrical cross section are standard equipment on multiple-track vehicles. A wide variety of tire sizes having different cross-sectional shapes regarding height-to-width ratios are used. In addition, there is a tendency to use tire cross-sectional shapes in which the height-to-width ratio (aspect ratio) is relatively small, which gives the tire a sporty look. An extreme example of this is racing car tires, which resemble rollers and have a very wide, almost flat tread. As a result, the contact area between the tire and the road is very large and, as the wheel load increases, greater longitudinal and lateral forces can be transferred.
The magnitude of the lateral forces that can be transferred is also dependent on the camber of the wheel in question and, in multiple-track wheeled vehicles, especially special-purpose vehicles known as xe2x80x9cKurvenlegerxe2x80x9d (three-wheeled vehicles that behave like two-wheeled vehicles when cornering), and also in production vehicles, this is utilized to good effect in that wheel suspensions are designed so that during jouncing the camber becomes negative, and combined with the increasing wheel load during cornering this results in greater transferable lateral guide forces for the wheels on the outside of the curve.
However, in conventional wheel suspensions the feasible negative camber range is very narrow, especially as, in the case of very wide sport tires, changes of this kind in the camber are undesirable in terms of the tires and are not particularly useful in terms of transferable guide forces, because, in the case of a tread with an essentially flat cross section, as the deviation from zero camber increases, the size of the contact area between the tire and the ground surface diminishes.
A pneumatic tire is described in Austrian Patent No. 255 919. The tire is asymmetrical in cross section and is designed for wheels where the camber is kept essentially constant via wheel control as part of the vehicle""s basic design. The goal is to achieve better driving characteristics and tire life because the tire is rounded in the shoulder area adjacent to the outside of the tire, in conjunction with the fact that the tread pattern varies across the tire""s cross section and/or the tread design varies with a view to achieving higher friction values or greater abrasion resistance. To this end, the largely flat tread section that extends to the inside of the wheel has a pronounced tread pattern for increased grip and includes abrasion-resistant tread material for high running performance in straight-line travel. By contrast, the rounded tread in the section adjacent to the outside of the wheel has a less pronounced tread pattern and includes tread material having a high friction value. This constitutes a good compromise in terms of a tire""s running and driving characteristics and its wear resistance.
A tire having an asymmetrical cross section in which the surface outline extending to the outside of the wheel has a slightly reduced diameter, which, when used with a constant-camber wheel suspension designed with negative camber, results in improved running characteristics along with reduced wear, is described in European Patent Application No. 0 607 784 A1.
Furthermore, pneumatic tires for wheels of multiple-track vehicles in which the sidewalls of the tire are of different heights, the outline of the tread being essentially symmetrical and flat, and the height of the tire sidewall on the inside of the wheel being smaller than the tire wall on the outside of the wheel, and accordingly the rim on the inside of a wheel having a larger diameter than the rim on the outside of the wheel, are described in U.S. Pat. No. 3,974,870, French Patent No. 2 200 122, and European Patent Application No. 0 607 784 A1.
The object of the present invention is to provide a pneumatic tire for wheels of multiple-track vehicles which, even if the tire is fairly wide and the vehicle is cornering, allows such a large contact area between a given tire and the ground that, in combination with increased wheel load during cornering, camber-related lateral forces which are well above the lateral forces that can be transferred with zero camber can be transferred, and allows different areas of the tread to be used in response to different driving and road conditions. The present invention provides a pneumatic tire for multiple-track vehicles, in particular motor vehicles, having a tread that forms the circumference of the tire and transitions into the sidewalls of the tire via laterally adjacent tire shoulders, the sidewalls extending radially inwards to beads that are attachable to the wheel rim, the tire being asymmetrical in cross section and the tread of the tire having a nearly flat tread section which extends from one sidewall area and transitions into a narrower convex tread section that extends radially inward to the other sidewall area, characterized in that the convex tread section (9) is assigned to the inside of the wheel and in the case of a negatively cambered wheel (1) forms the load-bearing tread section (9) with respect to the road (11).
Thanks to the asymmetrical design of the tire according to the present invention, the tire can be optimized to meet the requirements of driving in a straight line and normal driving, and also can be used in combination with an active camber control system and/or a closed-loop camber control system that allows one to convert the changes in wheel load associated with cornering in the form of increases in wheel load on the wheel on the outside of the curve into corresponding lateral guide forces, and when driving in a straight line it is possible to respond to specific circumstances such as winter driving by using a different section of the tread, so that as a result driving safety, including driving safety in extreme situations, can be improved.
In an embodiment according to the present invention, the contact area between a given tread and the road for the flat tread section when driving straight can be roughly equal to that for the convex tread section during cornering. In conjunction with adjusting the camber by an amount up to about 25xc2x0, it is particularly useful to design the tire so that negative camber of about 20xc2x0 in the wheels on the outside of the curve is feasible. According to this embodiment, the convex tread section facing the longitudinal middle of the vehicle is dimensioned so that in cross section the convex tread has a center plane or plane of symmetry which extends upwards and outwards at about 20xc2x0 to a radial plane and intersects the radial plane located at the transition from the flat tread section to the convex section at the center of curvature, in particular of the circle of curvature of the convex tread section.
According to the present invention, it is useful if the flat tread section that faces the outside of the vehicle and wheel constitutes at least 50%, but preferably about ⅗ to ⅘, of the width of the tread, so that the width of the convex tread section constitutes ⅕ to ⅖ of the total width of the tread. Even if a variety of different widths are optimal for the uses described above, a good rule-of-thumb is to use a width ratio such that the flat tread section constitutes ⅔ and the convex tread section ⅓ of the total width of the tread.
A circular arc shape is useful for the convex tread section, and the flat tread section should transition into the convex tread section that faces the middle of the vehicle. The radius of curvature of the convex tread section is preferably greater than its width, so that the convex tread section forms a relatively flat curve and can be roughly in the shape of a parabola. The radius of curvature of the convex tread section is preferably 1.25 to 1.75 times greater than the width of that part of the tread.
The radius of curvature of the convex tread section is ⅓-xc2xd as long as the total width of the tread.
The radius of curvature of the convex tread section is preferably greater than the height of the tire. The center of curvature preferably lies roughly within the radial plane of the tire on which the transition from the flat tread section to the convex tread section lies.
In the case of the convex tread section, the tire shoulder is preferably offset radially inwards relative to the shoulder adjacent to the flat tread section, this radial offset being about ⅙ to ⅓ of the tire height within the tire shoulder in question.
According to the present invention, the bead seats of the wheel that bears the tire can be radially offset by the same amount as the tire shoulders, so that a tire height on the inside of the wheel that is at least approximately equal to that on the outside of the wheel can be implemented.
Cambering the tire so that it runs on its convex tread section adjacent to the inside of the wheel has the consequence in terms of the forces perpendicular to the road that these forces act on the tire at the same angle as the negative camber that has been set, and thus result in a transverse force component that is high in terms of the tire""s support by the rim. As the tire has to meet many different load requirements, and must meet the usual standards in terms of comfort, driving behavior and the like, there may be problems associated with absorbing such a high transverse force component in the tire structure, unless otherwise undesired changes to the tire shape are made.
In an embodiment according to the present invention, in the area of the convex tread section, a support ring may be provided which is attached to the rim that bears the tire, and in the case of a non-cambered wheel separation is maintained relative to the tire""s inner surface and the support ring places limits on any undesired deformation of the tire and if necessary can be used as an additional load-bearing ring. It is particularly useful if, in the initial position, the distance between the tire and the support ring corresponds to the deformation path deemed permissible and/or the outline of the support ring that faces the tire""s inner surface corresponds to the desired shape of the tire.
If the support ring is designed to be partly elastic, the elastic design being particularly feasible for the seat of the support ring facing the tire, it is useful to design its elasticity and/or deformation behavior based on the aforementioned design goals, though in the initial position it may be necessary and useful to use, between the tire""s inner surface and the support ring and based on the tire""s deformation behavior, embodiments and separations relative to the tire""s inner surface whose arrangement in the initial position differs from that described above.
An embodiment according to the present invention, in which the convex tread section facing the inside of the wheel can be used via active camber control so that, for example, a winter tread can be used by cambering the tire during winter driving, and which also allows spikes to be arranged in the convex tread section, as this tread section is not used during normalxe2x80x94non-cambered wheelxe2x80x94driving operation and since, in view of the need to increase traction, switching over to this tread section while driving in a straight line is only an option in extreme cases. In conjunction with use of a support ring, according to the present invention one also has the option of providing retracted spikes such that the spikes are pushed into their extended work/grip position by the support ring if the wheel is cambered and the convex tread section is in contact with the support ring.
Thus there are many possible approaches to a tire according to the present invention in terms of using different tread patterns, different tread materials and the like, a particular advantage being that one can improve the vehicle""s behavior during aquaplaning by cambering the wheel and using the convex tread section.